Gas cooking grills and the like are usually constructed such that the source of gas (frequently a pressurized tank) and the burner are physically separated from one another. Such separation requires that a conduit be provided for connecting such source to the burner and flowing gaseous fuel thereto. Such conduits usually include a gas tube assembly which is flexible (to adapt to a variety of tank-burner positions) and which permits the introduction of air into the gas stream. Of course, the reason for introducing air is to provide the proper fuel-air mixture to result in clean, complete combustion. An example of such a tube assembly is shown in U.S. Pat. No. 4,827,899 (Walters et al.) and includes an air-entry aperture, the area of which is adjustable. Such adjustability is desirable when a burner is to be used with more than one type of fuel. Other examples of tube assemblies are shown in U.S. Pat. Nos. 4,679,544 (Koziol) and RE32,133 (Koziol--reissue of 4,373,505).
Another type of fuel-air mixer tube is shown in U.S. Pat. No. 4,827,903 (Kim). Such tube is now less common, notwithstanding its depiction in a relatively recent patent. Such tube includes a gently tapered hourglass-shaped venturi section having a length substantially greater than the diameter of the tube. An air entry port is spaced from the venturi section on the "downstream" end of the tube, i.e., that end of the tube nearer the burner. While venturi sections are know to accelerate the velocity of gaseous fuel flowing therethrough (and therefore lower its pressure), the illustrated port is at an area of maximum tube diameter where the velocity of the fuel has decreased to (or substantially to) its "pre-venturi" value. Such configuration has been found to be less than highly effective in introducing air into the gas stream--and of dubious value in causing good fuel-air mixing.
A gas burner is shown in U.S. Pat. No. 1,961,751 (Feyling). The Feyling device combines a burner with a mixer tube which is several times the diameter of the burner located at the upper end of the illustrated device. The Feyling burner to be used in an upright position, also has two or three restrictor portions, depending upon the variation under consideration. In either variation, the first restriction "necks down" the inlet passage while the second restriction includes a nozzle with a very small orifice. In one of the variations, the mixer tube is combined with a mixing chamber having an area of reduced diameter forming a third restriction. Such chamber gradually enlarges in diameter toward the burner "downstream" end. The Feyling patent explains that a straight mixer tube, i.e., one with a mixing chamber of uniform diameter, may also be used.
While one can only estimate the cross-sectional area of the orifice, its diameter appears to be less than 10% of that of the inlet upstream of it. Therefore, its area would be less than 1% of that of the inlet. Four air entry holes are provided adjacent to and downstream of the orifice-like nozzle. Such holes are to permit the entry of primary air to be mixed with gas and form a combustible mixture. In all configurations, the Feyling burner has projections at the top of the mixer tube to permit "secondary air" to flow to the top side of the flame to give "complete combustion." The Feyling device is not suitable for use with a remote burner--it is the burner.
U.S. Pat. Nos. 843,379 (Williams); 4,565,521 (Hancock) and the Kim patents all show devices in which the air entry port (or ports) are spaced from a restrictor portion and located downstream thereof. To put it another way, such ports communicate with the interior of the tube at a location where the interior cross-sectional area of such tube is unrestricted. Such port location is not at the region of highest gas velocity.
U.S. Pat. No. 4,738,614 (Snyder et al.) shows an atomizer for a post-mixer burner. The Snyder et al. atomizer includes a restrictor portion having a length about equal to the outer diameter of the device. Angularly-arranged atomizing passages are formed in the side wall to intersect the restrictor portion where such portion starts to enlarge toward its normal cross-sectional area. Liquid fuel flows in the main flow path while an atomizing fluid, e.g., steam or nitrogen, is introduced under high pressure through the atomizing passages in the side wall.